The present invention relates generally to an improved technique for the preparation of protein enriched yeast products, and more particularly to a method of producing such products from whey fermentation systems. The process of the present invention provides finished products which are high in protein content, low in ash and essentially free of carbohydrates, especially reducing sugars.
It is generally acknowledged that the world is entering an era of protein shortage. Accordingly, various techniques have been explored for the protein enrichment of food products both for human and animal consumption. Since the recognition of the fermentation process by Pasteur, considerable effort has been made to develop single cell protein systems to provide protein materials of high nutritional quality. Only modest gains have been made in accomplishing this goal due to the inherent limitations of the amino acid profiles of the various single cell protein. Bacteria are low in cystine and tryptophan, yeast are low in cystine and methionine, while algae are low in cystine, methionine and isoleucine content.
Of the various processes for producing single cell proteins, yeast is one of the more desirable microorganisms, since in most cases, proteins in the fermentation medium are either not utilized or only modestly utilized as a nutrient by the yeast. Consequently, a yeast fermentation is the process of choice in this invention, although the basic concept could be foreseeably applied with other microbial propagation processes where elimination of an undesirable constituent could be accomplished.
To maintain the protein quality of the enriched final product, cheese whey is the preferred fermentation substrate. There is currently over 30 billion pounds of liquid whey available annually in the United States of America and whey proteins are known for their exceptional nutritional quality. Whey from the manufacture of cheese contains most of the nutrients essential for yeast fermentation (respiration) and yeast products have already been shown to provide products with some applications in both foods for human consumption and for animal feeds.
Utilization of single cell protein products have been limited for a variety of reasons. Nucleic acid content must be restricted to less than 2 grams in the average dietary intake. The maximum protein content of single cell proteins is species specific in that bacteria may contain 47-87% protein; fungi (molds) 40%; yeast 50-54%; and algae only 40%. Cell walls and protein/ash ratios also reduce the amounts that can be used effectively in food systems, and these protein ingredients should additionally possess appropriate functional properties for promoting utilization. All of the essential amino acids must be present in adequate amounts to provide the desired quality for human and animal nutrition.
To overcome some of these impediments, the present practice includes blending microbial protein products with other ingredients. Milk, casein, caseinates, whey, modified whey, lactalbumin, soy concentrates and isolates, egg products, corn, wheat and other flours are typical of the ingredients used in these mixtures. However, an additional problem is encountered in that each of these ingredients contain varying amounts of carbohydrates. In particular, the milk or dairy products contribute the reducing sugar, lactose, to the blend and lactose intolerance is a problem in certain sectors. For certain animals and insects, lactose ingestion can result in growth retardation and even death. In the winter feeding of bees, for example, products containing lactose are considered lethal and cannot be used. In accordance with the present invention, however, residual carbohydrates are removed, and specifically residual lactose is removed from the finished product.
Another problem with residual carbohydrates in ingredients used in food product systems is the browning reaction due to the combination of reducing sugars with amino acids during heat treatments. Thus, a high protein content product devoid of reducing sugars can promote increased food utilization.
One system has partially satisfied the above parameters, wherein, in the fermentation of cheese whey, the whey portions (lactoglobulins) are coagulated (heat denatured) with these proteins being recovered with the yeast cells at the separation step. Even in this system (Mayer, B. M., 1970, Whey Fermentation. Proceedings Whey Utilization Conference, U.S.D.A.--ARS Publ. No. 76-36, p. 48), the yeast product contains only 57-60% protein. In accordance with the present procedure, however, higher protein contents are obtainable and, as previously indicated, residual carbohydrates are essentially removed.
In accordance with the present invention, therefore, the above limitations are essentially overcome. Any protein enriching substance may be added to the fermentation at an appropriate point in the process to allow removal (utilization by the cells) of the carbohydrates, while increasing the protein content and improving the amino acid balance of the final product. A wide variety of products are possible by this technique. Undenatured or denatured proteins, high protein/ash ratios and functional properties may be altered to satisfy specific requirements for use.